Comparison of the induction of cyclooxygenase and nitric oxide synthase by endotoxin in endothelial cells and macrophages

Endotoxin causes the expression of inducible nitric oxide (NO) synthase and cyclooxygenase-2. We have compared the ability of endotoxin to increase the activities of these enzymes in bovine aortic endothelial cells and the macrophage cell line (J774.2). Endotoxin (1 μg ml^-1; for 24 h) caused a time-dependent increase in the accumulation of cyclooxygenase metabolites from endogenous arachidonic acid, in both cell types. Cyclooxygenase activity towards exogenous arachidonic acid (30 μM; for 15 min) was also increased in both cell types. Endothelial cells and macrophages also contained comparable amounts of cyclooxygenase-2 protein after incubation with endotoxin for 24 h which was prevented by pretreatment with cycloheximide (10 μg ml^-1; 30 min prior to endotoxin). Endotoxin for 24 h caused a time-dependent increase in nitrite accumulation in macrophages, but not in endothelial cells. Thus, endotoxin increased cyclooxygenase activity and induced cyclooxygenase-2 protein in endothelial cells and macrophages. Endotoxin also increased NO synthase activity in macrophages, but not in endothelial cells.